1. Field of the Invention
The present invention relates to a pump for circulating a cryogenic fluid to feed the cryogenic fluid, and, more particularly, to a cryogenic fluid circulation pump that is capable of preventing heat from permeating into a cryogenic fluid by convection during the circulation of the cryogenic fluid by the pump and, at the same time, minimizing the transfer of heat to the cryogenic fluid circulating through a shaft rotating to rotate the pump.
2. Description of the Related Art
Generally, a cryogenic fluid is a fluid, such as general liquefied natural gas (LNG) or liquid oxygen, which is maintained at a sub-zero temperature of approximately −183° C. or less, although the temperature range is not definitely prescribed. It is required for a pump used to circulate and feed the cryogenic fluid to satisfy a requirement of minimizing the loss of the cryogenic fluid due to evaporation during the circulation of the cryogenic fluid considering a property of the cryogenic fluid.
However, a general fluid circulation pump is used under a condition of room temperature, and therefore, the general fluid circulation pump is not suitable for circulating a cryogenic fluid. For this reason, a pump capable of circulating and feeding the cryogenic fluid has been developed and used in recent years. A conventional cryogenic fluid circulating pump includes a housing constructed in a structure in which a cryogenic fluid is introduced through an impeller mounted inside the front thereof and is discharged through the side thereof. The impeller is connected to a drive shaft connected to a power source such that the impeller can rotate.
Also, a general mechanical seal or a labyrinth seal is mounted between the drive shaft connected to the impeller and the housing for preventing the leakage of the cryogenic fluid. The drive shaft, connecting the power source and the impeller, extends as long as possible to minimize the transfer of heat to the circulating cryogenic fluid.
In the conventional cryogenic fluid circulating pump with the above-stated construction, however, the housing in which the impeller is mounted is exposed to the atmosphere, with the result that the permeation of heat by convection is caused. Also, since the drive shaft, connecting the power source and the impeller, is very long to minimize the transfer of heat, the volume of the pump considerably increases.
Also, the mechanical seal or the labyrinth seal, mounted to minimize the leakage of the cryogenic fluid mounted between the housing and the drive shaft, is worn after the lapse of a specific period of use due to the continuous rotation of the drive shaft, with the result that, the leakage of the cryogenic fluid is caused.
For this reason, the conventional cryogenic fluid circulating pump is mainly used in an environment where heat loss and leakage are relatively ignored, i.e., a pump for LNG or a liquid nitrogen storage space.